1. Field of the Invention
The present invention relates generally to solid waste disposal. Solid waste disposal can be generally defined as the disposal of normally solid or semi-solid materials, resulting from human and animal activities, that are useless, unwanted, or hazardous. Solid wastes, therefore, typically may be classified in the following manner: "garbage" which is decomposable wastes from food; "rubbish" which is decomposable wastes, either combustible (such as paper, wood, and cloth) or non-combustible (such as metal, glass, and ceramics); "ashes" which is the residue of the combustion of solid fuels; "large wastes" which is demolition and construction debris and trees; dead animals; "sewage treatment solids" which is the material retained on sewage-treatment screens, settled solids, and biomass sludge; "industrial wastes" which includes such materials as chemicals, paints, and sand; "mining wastes" which includes slag heaps and coal refuse piles; and, "agricultural wastes" including farm animal manure and crop residues.
The present invention is primarily directed to the reduction, conversion, decomposition, and destructive distillation of garbage and rubbish (hereinafter collectively referred to as "household garbage") into useful by-products capable of being recycled and reused or otherwise transformed into useful articles.
2. Description of the Related Art
By far the most common method of disposing of solid wastes in the United States is the deposition of such wastes on land or in "landfills" which may account for more than ninety percent of the nation's municipal refuse. Incineration accounts for most of the remainder, whereas composting of solid wastes accounts for only an insignificant amount. Historically, a municipality's chosen disposal method depended almost entirely on costs, and more recently environmental conditions, both of which in turn are likely to reflect the local circumstances.
A sanitary landfill is the cheapest satisfactory means of disposal, but only if suitable land is within economic range of the source of the wastes. Typically, collection and transportation costs account for seventy-five percent of the total cost of solid waste management. In a modern landfills, refuse is spread in thin layers, each of which is compacted by heavy industrial equipment such as bulldozers before the next layer is spread. When about 3 meters of refuse has been laid down, it is covered by a thin layer of clean earth which also is compacted. Pollution of surface and groundwater is believed to be minimized by lining and contouring the fill, compacting and planting the cover, selecting proper soil, diverting upland drainage, and placing wastes in sites not subject to flooding or high groundwater levels. Gases are generated in landfills through anaerobic decomposition of organic solid waste. If a significant amount of methane is present, it may be explosive; therefore, proper venting and burning of the methane gases are often necessary to eliminate or alleviate these dangerous conditions.
Another method of solid waste disposal is incineration. Incinerators of conventional design burn refuse on moving grates in refractory-lined chambers. The combustible gases and the solids they carry are burned in secondary chambers. Combustion is eighty-five to ninety percent complete for the combustible materials. In addition to heat, the products of incineration include the normal primary products of combustion including carbon dioxide and water, as well as oxides of sulfur and nitrogen and other gaseous pollutants. The nongaseous products are fly ash and unburned solid residue. Emissions of fly ash and other particles are often controlled by wet scrubbers, electrostatic precipitators, and bag filters. Incineration methods of disposing of cellulose material take the cellulose material to the burning point which is known to destroy the hemicellulose sandwiched between the lignin and cellulose components of woody cellulose materials (see the explanation set forth below) thereby breaking the bonds comprising the cellulose material which, in turn, allow it to rapidly degrade.
Landfill and incineration methods of disposal are known to pose significant environmental problems and concerns for the municipality, government, private industry, and individuals.
A growing trend associated with the treatment and handling of solid waste material may be referred to here as "resource recovery". Resource recovery systems are intended to recover useful materials from raw municipal refuse (e.g., household garbage) and may include grinding or shredding machines, magnetic separators, air classification that separates the light and heavy fractions, screening, and/or washing. Resource recovery methods, therefore, attempt to reduce (i.e., recycle) the solid waste into a more manageable, although not always useful, form. Resource recovery systems can be considered thermal processes, generally, but more specifically, a combustion processes or pyrolysis processes. The cellulose element can be defined as the chief substance composing the cell walls or woody part of plants. Cellulose is known to be a carbohydrate of unknown molecular structure but having the composition represented by the empirical formula (C.sub.6 H.sub.10 O.sub.5).sub.x. Prior to the creation of the present invention, a constituent element of "woody" cellulose materials, hemicellulose, which serves as the binding agent for the constituent elements of the wood-like cellulose molecule, has been destroyed by known resource recovery methods. The other constituent elements of woody cellulose materials are lignin and cellulose.
Lignins are major constituents of plant matter. Lignins can be defined as an organic substance closely allied to cellulose and forming the essential part of woody fibers. On the basis of chemical and biological degradations, lignins are considered to be polymers or prophyl-phenyl compounds, coniferyl and related alcohols. Over the years solubilization techniques have been suggested as tools for deducing the structure of coals, oxidation, hydrogenation, alkaline hydrolysis, pyrolysis and extraction with powerful solvents.
With respect to the ability to disassociate the hemicellulose from cellulose-containing materials, these techniques are believed to be of limited utility considering their harsh and destructive nature. Furthermore, the known methods of disassociation incorporating the use of solvents and oxidants often pose environmental concerns and for this reason are also not particularly desirable.
Hemicellulose constitutes from 35% to 50% of the polysaccharides in the cell wall substance of cellulose fibers and from 20% to 35% of the total dry weight of the wall fibers. The definition of hemicellulose is even less precise than that of most other plant constituents and is based mainly on chemical behavior.
The hemicellulose is composed of two general classes of substances: (1) those collectively called xylons whose molecules are formed by polymerization of the anhydro forms of pentose sugar; 22 and, (2) glucomannans, whose molecules are formed by polymerization of anhydro forms of hexose, mainly glucose and mannose. These "sugars" and elements having amino acid bases or subconstituents are not readily disassociated without destroying them. Combustion processes and pyrolysis processes are known to destroy or deform the constituent sugars and amino acids (in exothermic reactions), thereby eliminating the ability to disassociate them and recombine them in a resource-recovery-like manner. In this way the sugars and amino acids act as bonding agents for cellulose molecules even though the sugars and amino acids bases did not originate from materials typically associated with cellulose. That is, combustion and pyrolysis processes are known to destroy the hemicellulose and prevent its use as a bonding agent to form other molecules of cellulose, even though the hemicellulose did not originate from recognizable cellulose materials, e.g., cardboard, paper, wood, etc.
With respect to the ability to recombine the disassociated hemicellulose with the other constituent elements of are cellulose fibers and particles, hemicellulose has three known attributes which enable it to aggregate in polar liquid.
First, the shape of the hemicellulose molecule is a uniform ribbon-like structure with a crosssection similar to plastic-like fibers. Second, the carbon-to-carbon bonding gives high rigidity and coherence; and third, the numerous hydroxyl (OH) groups are available along the length of the molecule to lateral bond chains of fly ash and other polymers. As a result, the hemicellulose fibers have a tendency to become closely packed and regularly spaced along parts of their length with their flat faces sandwiched together. These regions of high molecular orientation have diffraction patterns similar to crystalline solids. In addition, the hemicellulose extracted pursuant to the method of the present invention may also contain impurities in the form of bacteria that is trapped in the interstices of the hemicellulose.
Pyrolysis, also called destructive distillation, is the process of chemically decomposing solid wastes by the introduction of heat in an oxygen-reduced atmosphere. This results in a gas stream containing primarily hydrogen, methane, carbon monoxide, carbon dioxide, and various other gases and inert ash, depending on the organic characteristics of the material being pyrolyzed. The hemicellulose in these pyrolysis processes is destroyed.
Yet another approach to the treatment of raw municipal refuse (e.g., household garbage) is know as a "wet pulping process". In a wet pulping process the incoming refuse is mixed with water and ground into a slurry in an apparatus referred to as a wet pulper--a machine that is similar to a large kitchen disposal unit. Large pieces of metal and other non-pulpable materials are separated by a magnetic separator, and the residue is used as landfill. The slurry from the pulper goes into a centrifugal device called a liquid cyclone, which separates heavier non-combustibles such as glass, metals, and ceramics. The heavy fraction goes to a glass and metal recovery system; the light fraction goes to a paper and fiber recovery system. Combustible residues are mixed with sewage sludge, mechanically dewatered, and incinerated. Noncombustible residues are used as landfill.
The art to which the invention relates generally includes U.S. Pat. No. 4,012,231 granted to Dreer, incorporated by reference as if fully set forth herein, is directed to a process for the manufacture of fillers from solid waste. The Dreer invention can be described as a wet-pulping process of grinding solid waste magnetically freed from iron particles, supplied with sewage sludge or water, fractionated into portions of different size and treated in a fermentation process for about 24 hours. Various solvents and reactant solutions or materials are then used to transform the compost.
In all known methods of solid waste reduction, treatment or resource recovery, the resultant product (i.e., end or by-products) of the solid material may include microbes or microorganisms that require further consideration prior to disposal. In such cases the by-products are believed to remain waste materials not suitable for use or transformation into useful articles. Furthermore, the useful hemicellulose material is known to be destroyed to a large degree and thus wasted, because it is not reused to form other useful substances.
The present invention, including its apparatuses and methods, relate generally to resource recovery methods, and some of the physical characteristics associated with the thermodynamic processes of destructive distillation, wet pulping, decomposition, and sterilization. Until now, a resource recovery apparatus and method of incorporating select elements of the aforementioned processes or systems into an efficient, safe and economical resource recovery system, wherein the end by-products including hemicellulose, cellulose and other organic fibers capable of being reused, has not been invented.